Z-stage with dynamically driven stage mirror and chuck assembly

ABSTRACT

Substrate support apparatus and methods are described. Motion of a substrate chuck relative to a stage mirror may be dynamically compensated by sensing a displacement of the substrate chuck relative to the stage mirror and coupling a signal proportional to the displacement in one or more feedback loops with Z stage actuators and/or XY stage actuators coupled to the stage mirror. Alternatively, a substrate support apparatus may include a Z stage plate a stage mirror, one or more actuators attached to the Z stage plate, and a substrate chuck mounted to the stage mirror with constraints on six degrees of freedom of movement of the substrate chuck. The actuators impart movement to the Z stage in a Z direction as the Z stage plate is scanned in a plane perpendicular to the Z direction. The actuators may include force flexures having a base portion attached to the Z stage plate and a cantilever portion extending in a lateral direction from the base portion. The cantilever portion may include a parallelogram flexure coupled between the base portion and a free end of the cantilever portion.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims priority from co-pending provisional patentapplication Ser. No. 60/745,384, which was filed on Apr. 21, 2006, theentire disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention generally relates to substrate processing and moreparticularly to substrate supports for substrate processing.

BACKGROUND OF THE INVENTION

Modern semiconductor systems often depend on accurate measurement of theposition of a semiconductor substrate. An example of a tool commonlyused in semiconductor wafer metrology and inspection is an electronmicroscope. FIG. 1 depicts an electron beam microscope system 100 of theprior art. An electron optical column 102 focuses an electron beam 101onto a surface of a wafer 104. Electrons scattered from the wafer 104are collected to form an image. To facilitate location of defects ondifferent parts of the wafer 104, the wafer is typically processed on asupport 105 having a chuck 106 and XY stage 108 for translation of thechuck (and wafer) in X and Y directions more or less parallel to theplane of the wafer 104. Since the electron beam microscope 100 mustoperate in a vacuum chamber 103, the chuck 106 is typically a highvoltage electrostatic chuck. The change in position of the wafer 104 canbe measured using an interferometer system 112 measuring off a stagemirror 110. The stage mirror 110 includes highly polished faces 114oriented perpendicular to the X and/or Y axes. In the interferometer 112a beam of light 116 (e.g., from a laser) is split by a beamsplitter 118.Part of the light (referred to sometimes as the reference beam) reflectsoff a fixed mirror 120 back to the beamsplitter 118. Another part of thelight (referred to sometimes as the measured beam) reflects off thehighly polished face 114 back to the beamsplitter 118. The beamsplitter118 combines both parts and the combined optical signal strikes aphotodetector 119. An interference signal from the photodetector 119changes in a predictable way as a result of movement of the stage mirror110.

As the wafer 104 moves in the X and Y the depth of focus of the electronbeam 101 may vary as a result of topographical features or tilting ofthe surface of the wafer 104. To adjust for variations in topography ofthe wafer surface the support 105 may include a Z stage 122. The Z stage122 includes a stage plate 124, one or more piezoelectric actuators 126.The wafer chuck 106 is attached to the Z stage plate 124 by compliantmounts 128. High voltage electrical isolators 130 provide electricalinsulation between the chuck 106 and the Z stage plate 124. The stagemirror 110 is mounted to the Z stage plate 124 through kinematic mounts132, e.g., of the sphere and V-groove type, the sphere and cone typeand/or the sphere and flat type. In many prior art systems, the wafersurface is analyzed to determine a slope and then the Z stage 122 ismoved up or down to level the wafer statically. Such systems can notdynamically adjust the height of the wafer 104 in response to changingwafer topography.

Furthermore, the Z stage 122 carrying the wafer chuck 106 ismechanically separated from the stage mirror 110, which typically isrigidly coupled to the XY stage 108. As a result of this mounting thereis a long mechanical path indicated by the dashed line 134 (sometimesreferred to as a metrology loop) between the polished surface 114 on thestage mirror 110 and the wafer chuck 106. Due to this long path staticand dynamic XY position errors due to relative motion between the waferchuck 106 and the stage mirror 110 are properly not tracked by theelectron beam 101. Instead, these errors are tracked by image computeralignment at a relatively slow bandwidth. These errors include scan toscan errors, intra-scan errors and high frequency (kernel to kernel)errors. In systems such as that shown in FIG. 1, a position sensor 136,e.g., a capacitor gauge, placed proximate the wafer chuck 106 may beused to characterize these errors by measuring a relative displacementΔX between the chuck 106 and the stage mirror 110.

In alternative prior art designs, e.g., the Mebes Exara, designed byEtec systems, a substrate (e.g., a mask) may be coupled to the stagemirror 110, but is pre-aligned prior to scanning the mask in the X and Ydirections and is not dynamically adjusted in the Z direction during thescan. In this design, static pre-alignment of the substrate is mappedprior to the scan and is not dynamically adjusted into the optical focalplane during the scan. Thus, changes in height have to be compensated bysome other means.

Prior art attempts to address tracking errors due to relative motionbetween the substrate chuck 106 and the stage mirror 110 have beenlimited by the bandwidth of the deflection system, interferometer datarate and data age. These errors may be large enough to case either afalse defect detection or loss of inspection sensitivity.

Thus, there is a need in the art, for a substrate support system thatovercomes these disadvantages.

SUMMARY OF THE INVENTION

The disadvantages associated with the prior art are overcome byembodiments of the present invention directed to substrate supportapparatus and methods.

According to an embodiment of the invention, motion of a substrate chuckrelative to a stage mirror may be dynamically compensated by sensing adisplacement of the substrate chuck relative to the stage mirror andcoupling a signal proportional to the displacement in one or morefeedback loops with means for dynamically compensating for motion of thesubstrate chuck relative to the stage mirror. The means for dynamicallycompensating may include Z stage actuators and/or XY to the stage mirrorand/or XY energetic-beam deflection mechanisms.

According to an alternative embodiment of the invention a substratesupport apparatus may include a Z stage plate, a stage mirror, one ormore actuators attached to the Z stage plate, and a substrate mounted tothe stage mirror with constraints on six degrees of freedom of movementof the substrate chuck. The actuators are configured to impart movementto the Z stage in a Z direction as the Z stage plate is scanned in oneor more directions in a plane perpendicular to the Z direction. Theactuators may include force flexures. Each force flexure may include abase portion attached to the Z stage plate and a cantilever portionextending in a lateral direction from the base portion. The cantileverportion may include a parallelogram flexure coupled between the baseportion and a free end of the cantilever portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a schematic side-cross section of a substrate support systemused in conjunction with an electron microscope of the prior art.

FIG. 2 is a schematic diagram is a schematic side-cross section of asubstrate support system according to an embodiment of the presentinvention.

FIGS. 3A-3B are cross-sectional schematic diagrams of substrate supportsystems according to alternative embodiments of the invention.

FIG. 4A is a three-dimensional view of a force flexure that may be usedwith the substrate support system of FIG. 3A.

FIG. 4B is a cross-sectional view of the force flexure of FIG. 4A takenalong line B-B′

FIG. 5A is a cross-sectional schematic diagram of a substrate supportsystem according to an alternative embodiment of the invention.

FIG. 5B is a plan view of the substrate support system of FIG. 5A.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Although the following detailed description contains many specificdetails for the purposes of illustration, anyone of ordinary skill inthe art will appreciate that many variations and alterations to thefollowing details are within the scope of the invention. Accordingly,the exemplary embodiments of the invention described below are set forthwithout any loss of generality to, and without imposing limitationsupon, the claimed invention.

According to a first embodiment of the present invention, a conventionalsubstrate support system of the type shown in FIG. 1 may be modified bycoupling a feedback signal from a chuck position sensor to a closed loopdrive that moves an energetic beam (e.g., the electron beam 101) in XYand/or actuators of the Z stage to compensate for motion of chuck 106relative to stage mirror 110. As shown in FIG. 2, a substrate supportsystem 200 may include many of the features described above with respectto FIG. 1. Features common with the support system 100 of FIG. 1 areidentified by the same numbers shown in FIG. 1 FIG. 2. The substratesupport system 200 includes a Z-stage 122 having a Z-stage plate 124,and Z-actuators 126. A substrate support chuck 106, e.g., anelectrostatic chuck, is compliantly connected to a Z stage plate 124,e.g., by flexures 128. Preferably, the flexures 128 are characterized byhigh stiffness with respect to motion in the X-Y plane and rotationabout Z-axis constraints while allowing the chuck 106 to move along theZ-axis.

The Z stage 122 is mounted to an XY stage 140, having an X-stage 142 anda Y-stage 144. Preferably, the coupling between the Z-stage 122 and theX-Y stage 140 is characterized by high stiffness with respect to motionin the X-Y plane and rotation about Z-axis constraints while allowingthe Z-stage to move along the Z-axis. The X stage 142 includes an Xactuator 146 that provides an actuation force in an X-direction. The Ystage 144 includes a Y actuator 148 that provides an actuation force ina Y-direction that is, e.g., perpendicular to the X-direction. A stagemirror 110 is kinematically mounted to the Z stage plate 124, e.g., withthree ball and groove type mounts 132. The stage mirror 110 may includepolished surfaces 114 that can be used as reflecting surfaces for aninterferometer 112. Z actuators 126 (e.g., piezoelectric actuators)provide actuating forces that move the chuck 106 relative to the Z stageplate along a Z-direction that is normal (i.e., perpendicular) to the X-and Y-directions. The substrate chuck 106, stage mirror 110, and Z stage122 may be disposed within a vacuum chamber 103.

One or more relative position sensors 136 are configured to sense adisplacement of the substrate chuck 106 relative to the stage mirror 110with respect to the X- and/or Y- and/or Z-directions. By way of examplethe chuck 106 may move in the X-direction by an amount X₁ while thestage mirror 110, moves by a different amount X₂. One sensor 136 maysense the relative displacement ΔX=X₁-X₂. Other sensors 136 maysimilarly sense relative displacement in the Y and Z directions. Thesensors 136 may be any suitable motion sensor, e.g., a capacitive,inductive or optical sensor. By way of example, the position sensors 136may be capacitance sensors mounted to the stage mirror 110 proximate thesubstrate chuck 106. The capacitance sensors may produce a signal thatdepends in a determinable way on a relative displacement between thechuck 106 and the stage mirror 110. It is noted that the interferometer112 may be regarded as a form of optical relative position sensor. Therelative position sensors 136 and/or photo detector 119 of theinterferometer 112 may be coupled in one or more outer feedback loops150 to one or more of the actuators 126, 146, and 148 so that theactuators can dynamically compensate for motion of the substrate chuck106 relative to the stage mirror 110. In certain embodiments of theinvention it is desirable to have one sensor proximate the metrologyloop 134 described above with respect to FIG. 1 and one or more sensorsco-located with the actuators. One or more additional relative positionsensors 136′ may be built into the Z-actuators 126 and/or XY stageactuators 146, 148.

For fine position correction of the electron beam 101 an XY beamdeflection mechanism 107 (e.g., electrostatic beam deflector plates orbeam-deflecting electromagnets) in the electron optical column 102) iscoupled via an inner feedback loop 152 to the photo detector 119 of theinterferometer 112 and/or the position sensors 136. The inner feedbackloop 152 allows for fine XY correction of the position of the electronbeam 101 on the wafer 104. Those of skill in the art will recognize thatthe same concept may apply to beam position correction for otherenergetic beams, such as ion beams (e.g., using electrostatic orelectromagnetic beam deflection), laser beams (e.g., using beam steeringmirrors as the correction mechanism 107) and the like.

In some applications, e.g., where the system 200 is used for substratesupport in an electron beam the stage control loop (e.g., outer feedbackloop 150 and actuators 146, 148 may be burdened with a large followingerror, e.g., between about 100 nm and about 2 microns. If the systemneeds images aligned to about 1/10 of a pixel, two more controlmechanisms may be employed: beam deflection following a stage mirrorposition signal from the interferometer 112 and/or additional chuckposition sensor 136, and an image computer (not shown), performingdynamic alignment of images, to the extent the other mechanisms leaveany residuals. The computer may be able to correct position errors in arange from about 250 nanometers (nm) down to about 2.5 nm. The positionsignal from the interferometer 112 may be fed back to the stage controlactuators 146, 148, which can make position adjustments on the order ofa few hundred millimeters down to about 2 microns. The stage controlactuators may leave a residual of a few microns. If the stage feedbackloop is relatively slow (e.g., tens of Hz) the outer feedback loop 150and stage actuators 146, 148 may not be fast to correct image jitter onthe order of 250 nm to 2 microns coming from roller vibration and othersources. The gap may be filled by e-beam correction, which has a muchhigher speed, e.g., about 10 kHz, and accuracy of single nanometers orbetter. Presently available interferometers may be accurate to about 0.1nm, but mechanical and electrical noise may bring this up to about 2 nm.

In other embodiments of the present invention, the metrology loop may beshortened and the relative displacement between the substrate chuck 106and the stage mirror 110 may be substantially reduced by directlymounting the chuck to the stage mirror. This has not been done in asystem that can scan in the Z-direction. This has largely been due tothe relatively large mass of the substrate chuck. A Z-stage withsufficiently strong actuators and sufficiently stiff flexures had notpreviously been developed. Generally, it is desirable to usepiezoelectric actuators for substrate supports in electron beam systems.Voice coil actuators typically are not used since they produce magneticfields that can interfere with the electron beam. Voice coil actuatorscan be used if they are sufficiently magnetically shielded and/orpositioned far away from the electron beam. Direct Z-actuation by apiezo stack would require a relatively long piezo actuator and arelatively long compliant flexure to produce the desired Z-displacement.As a result, the stage mirror and chuck would tend to wobble in the X-Yplane.

FIG. 3A depicts a substrate support apparatus 300 according to analternative embodiment of the present invention. The apparatus 300generally includes a Z stage plate 322, a stage mirror 310 and asubstrate chuck 306. The Z-stage plate 322 may be attached to an XYstage 308 that can scan the Z stage plate 322, stage mirror 310 andsubstrate chuck 306 in an X-Y plane. The chuck 306, stage mirror 310,Z-stage plate 322 and XY stage 308 may be located in a vacuum chamber303 so that the apparatus 300 can be used, e.g., in conjunction with anelectron beam or ion beam system. In an alternative embodiment depictedin FIG. 3B, the stage mirror 310 may be built into the substrate chuck306.

An energetic beam column 302 produces an energetic beam 301 directed ata substrate 304 on the substrate chuck 306. An XY beam deflectionmechanism 307 steers the energetic beam 301 in the XY plane (i.e., theplane of the substrate 304). By way of example, the energetic beamcolumn 302 may be an electron beam column, in which case the energeticbeam 301 is a beam of electrons. Alternatively, the energetic beamcolumn 302 may be an ion optical column or an optical column producingsome form of energetic electromagnetic radiation, e.g., infrared,visible or ultraviolet light. In the case of an electron or ion opticalcolumn, the XY beam deflection mechanism 307 may include electrostaticdeflector plates or electromagnets or some combination of both. In thecase of an infrared, visible or ultraviolet optical column (e.g., basedon a laser as a source of electromagnetic radiation) the XY beamdeflection mechanism 307 may include a beam steering mirror.

One or more sensors 336, e.g., capacitance sensors, may be placedproximate the substrate chuck 306 to measure relative motion between thechuck 306 and the stage mirror 310. The sensors 336 and/or aninterferometer photo detector 319 may be coupled to actuators 346 on theXY stage in an outer feedback loop 350 as described above. Similarly,the photo detector 319 and/or sensors 336 may be coupled to a beamdeflection mechanism 307 by an inner feedback loop 352 as describedabove.

The chuck 306 may be a bi-polar or mono-polar electrostatic chuck. Thestage mirror 310 may be made of an electrically insulating material suchas alumina. Alternatively, electrically conductive or semi-conductivematerials such as silicon carbide may be used. The stage mirror 310includes highly polished faces 314 oriented perpendicular to the Xand/or Y axes. The highly polished faces 314 serve as reflectingsurfaces for an interferometer 312 having a beamsplitter 318, a fixedmirror 320 and a photodetector 319. The beamsplitter 318 splits a beamof light 316 (e.g., from a laser). Part of the light 316 reflects offthe fixed mirror 320 back to the beamsplitter 318. Another part of thelight reflects off the highly polished face 114 back to the beamsplitter118. The beamsplitter 118 combines both parts and the combined opticalsignal strikes a photodetector 119. An interference signal from thephotodetector 119 changes in a predictable way as a result of movementof the stage mirror 110.

The substrate chuck 306 may be mounted to the stage mirror 310 withconstraints on six degrees of freedom of movement of the chuck 306relative to the stage mirror 310. By way of example, the chuck 306 maybe kinematically mounted to the stage mirror 306 through a sphere andcone mount, a sphere and groove mount and a sphere and flat mount.Kinematic mounting generally refers to a mount that places independent(i.e., non-redundant) constraints on the six degrees of freedom(translation along the X, Y and Z directions and rotation about the X, Yand Z axes). In an example of kinematic mounting the stage mirror 310may be mounted to the Z stage plate 322 with sphere and V-groove typemount, a cone and sphere type mount and a sphere and flat type mount.The constraints on the chuck 306 need not be strictly kinematic. Forexample, the chuck 306 may be mounted by three sphere and groove mountswith the grooves being aligned at 120° angles relative to each other.The spheres can be the supports, and the V-grooves can be formed in theback of the chuck 306. A scheme with three V-grooves supporting thechuck with three spheres is fully kinematic, as is the scheme with acone (or trihedral hollow), a vee, and a flat, supporting a chuck withthree spheres. These two schemes are equivalent, but differ in thebalance of forces and dynamics. The three V-groove scheme has betterbalance due to symmetry. Alternatively, the chuck 306 may be rigidlyattached to the stage mirror 310, e.g., with bolts or screws or thechuck 306 may be built into the stage mirror 310 or the stage mirror 310may be built into the chuck 306, e.g., as illustrated in FIG. 3B.Preferably, the flexures 400 are characterized by high stiffness withrespect to motion in the X-Y plane and rotation about Z-axis constraintswhile allowing the stage mirror 310 to move along the Z-axis.

One or more force flexures 400 couple the stage mirror 310 to the Zstage plate 322. The force flexures 400 include actuators configured toimpart movement to stage mirror 310 and substrate chuck 306 in a Zdirection as the Z stage plate 322 is scanned in the X-Y planeperpendicular to the Z direction. With two or more force flexures 400,independent adjustment of the Z-deflection of each force flexure 400provides tilt control of the stage mirror 310 and the substrate chuck306.

As shown in FIGS. 4A-4B each force flexure 400 includes a base portion402 and a cantilever portion 404. The base portion 402 is secured to theZ stage plate 322 by suitable means such as bolts or screws. Thecantilever portion 404 extends in a lateral direction (e.g., the X or Ydirection) from the base portion 402. The cantilever portion 404includes a parallelogram flexure 403 coupled between the base portion402 and a free end 406 of the cantilever portion 404. The base portion402 and cantilever portion 404 (including the parallelogram flexure 403)may be integrally formed from a single block of material. The materialis preferably one that provides high strength, high electricalresistivity, and a relatively high stiffness to mass ratio. It is alsodesirable for the material to have a high ration of yield strength toYoung's modulus. Titanium is an example of a suitable material.

The parallelogram flexure 403 includes an upper arm 408 and a lower arm410. The upper and lower arms 408, 410 are substantially parallel toeach other. The upper arm is spaced apart from the lower arm 410 alongthe Z direction by a distance c. A lever block 412 depends from theupper arm 408. A channel 414 separates the lever block is separated fromthe base portion 402, free end 406 and lower arm 410. A first resilienthinge 416 connects the upper arm 408 to the base portion 402. A secondresilient hinge 418 connects the upper arm 408 to the free end 406. Athird resilient hinge 420 connects the lower arm 410 to the base portion402. A fourth resilient hinge 422 connects the lower arm 410 to the freeend 406. The first and second hinges 416, 418 are separated by a lateraldistance a. Similarly, the third and fourth hinges 420, 422 areseparated b from each other by an approximately equal lateral distancea. The hinges 416, 418, 420, 422 may be formed by suitably thing thematerial at the junctures between the upper and lower arms 408, 410 andthe base portion 402 and/or free end 406. An isolator 405 made of anelectrically insulating material may connect the free end 406 to thestage mirror 310.

As a result of the configuration of the arms and hinges of thecantilever portion 404 a laterally directed force F acting on the leverblock 412 causes the free end 406 to move in the Z-direction. Such alateral force F may be provided in a controllable fashion by apiezoelectric actuator 424, which may be located in a bore 426 in thebase portion 402 and secured in place with a threaded plug 428. Thepiezoelectric actuator 424 can expand laterally against the lever block412. The piezoelectric actuator 424 may include a joint end with acurved (e.g., spherical) surface 430 that abuts the lever block 412. Theend surface 430 makes contact with the lever block 412 at a pointlocated a distance b from the upper arm 408. The curved surface 430 ofthe joint end is desirable to keep the piezoelectric actuator frombending. The ratio b/a determines the leverage and stiffness of theparallelogram flexure 403.

The parallelogram flexure 403 and lever block 412 allows the lateralforce F to be converted into vertical motion of the free end 406 of thecantilever 404. Thus a relatively long piezoelectric actuator 424 may beused in a force flexure 400 of limited height. This combination makesthe force flexures relatively stiff and strong. A typical piezoelectricstack may produce about 1 micron of lateral expansion for eachmillimeter of stack length. Thus a 100 millimeter piezoelectric actuator424 may expand by about 100 microns. By a suitable choice of b and a theforce flexure 400 can transfer 100 microns of piezoelectric actuatorexpansion into about 300 microns of movement of the free end 406. Thedesign of the force flexure 400 provides for a high lateral stiffness,which creates a good coupling of the stage mirror 310 to the XY stage308. The Z stiffness of the force flexure 400 also allows for a highbandwidth of control of motion in the Z-direction.

Other types of piezo-based actuators are suitable as alternatives to thepiezoelectric actuator 424 provided they meet the dynamic and magneticrequirements. For example, voice coil type actuators may be used insteadof piezoelectric actuators. In electron beam applications voice coiltype actuators may need to be magnetically shielded to avoid disturbingthe electron beam.

A substrate support apparatus of the type shown in FIG. 3A using forceflexures of the type shown in FIGS. 4A-4B provides considerably improvedperformance compared to a prior art type substrate support of the typedepicted in FIG. 1. Untracked errors in a prior art system of the typeshown in FIG. 1 have been measured to be on the order of about 100 nm.In a substrate support of the type shown in FIG. 3A, by contrast,tracking errors resulting from small dynamic parasitic motions of thewafer chuck 306 relative to the stage mirror 310 have been measured tobe on the order of 0.1 nm standard deviation, an improvement of aboutthree orders of magnitude. Tests comparing scan-to-scan errors,intra-scan errors and kernel-to-kernel errors for the two types ofsubstrate supports have also been performed. The results of these testsare summarized in TABLE I below.

TABLE I FIG. 1 Type FIG. 3A Type Spec (nm) Apparatus ApparatusScan-to-scan 150 200-350 20-30 Intra-scan 150 20-60 3.2 Kernel-to-kernel3 25-30 2

The scan to scan error includes wafer and chuck shifts due to end ofswath turnaround deceleration and acceleration. It is the averageuntracked error between the wafer and the interferometer mirror.

The intra-scan error is measured as a shift between the chuck and thestage mirror while the stage is scanning at a constant velocity. Thechuck is only subject to vibrations caused by stage bearings

The image correction is based on small fragments of a swath calledkernels. In this case the kernel contains 48 vertical scan lines, eachline acquired every 12 microseconds. The line frequency is 83.3 kHz, andthe kernel frequency is 1736 Hz. The image is realigned at the kernelfrequency; therefore the kernel to kernel error is the residual errorwhich the image computer's alignment system has to deal with.

It is noted that all the errors for the FIG. 1-type apparatus variedfrom test to test. Furthermore, the scan-to-scan error values for theFIGS. 3A-type apparatus appeared only when the apparatus was jolted bygreater than about an acceleration of about 5 m/s² (about half theacceleration due to gravity). Embodiments of the present invention mayinclude alternative actuators and flexures to those shown in FIG. 3A andFIGS. 4A-4B. For example, as shown in FIGS. 5A-5B, a substrate supportapparatus 500 may have a stage mirror 510 coupled to a Z-stage plate 522with vertical piezoelectric actuators 526. The stage mirror 510 mayinclude highly polished surfaces 514, which may be used as reflectingsurfaces for interferometers. A chuck 506 may be rigidly orkinematically mounted to the stage mirror 510 as described above. TheZ-stage plate 522 may be attached to an XY stage 508. One or moreactuators 526 may be coupled directly between the Z-stage plate 522 andthe stage mirror 510. By way of example, the actuators 526 may bepiezoelectric actuators that expand in the Z-direction. One or moreconstraints 525 may be coupled between the Z-stage plate 522 and thechuck and/or stage mirror 510. The constraint 531 is configured torestrict movement of the stage mirror 510 and/or chuck 506 in one ormore directions perpendicular to the Z-direction. By way of example, theconstraints 531 may each include a V-groove 533 parallel to theZ-direction. A spherical bearing 535 is disposed between the V-groove533 and a recess 537 in the stage mirror 510.

An energetic beam column 502 produces an energetic beam 501 directed ata substrate 504 on the substrate chuck 506. An XY beam deflectionmechanism 507 steers the energetic beam 501 in the XY plane (i.e., theplane of the substrate 504). By way of example, the energetic beamcolumn 502 may be an electron beam column an ion optical column or anoptical column producing some form of energetic electromagneticradiation, e.g., infrared, visible or ultraviolet light.

One or more sensors 536, e.g., capacitance sensors, may be placedproximate the substrate chuck 506 to measure relative motion between thechuck 506 and the stage mirror 510. The sensors 536 and/or a photodetector 519 of an interferometer 512 may be coupled to actuators 546 onthe XY stage in an outer feedback loop 550 as described above.Similarly, the photo detector 519 and/or sensors 536 may be coupled to abeam deflection mechanism 507 of the energetic beam column 502 by aninner feedback loop 352 as described above.

As can be seen from Table I above, embodiments of the present inventionprovide reduced scan-to-scan, intra-scan and kernel-to-kernel errorscompared to prior art substrate support apparatus. Embodiments of thepresent invention are particularly well-suited to applications that aresensitive to motion of the substrate in a direction perpendicular to aplane of the substrate. Examples of such applications include, but arenot limited to wafer inspection, reticle inspection, lithography orreticle printing. Embodiments are also particularly well-suited for usein vacuum including electron microscopy, ion beam machining, electronbeam machining and the like.

While the above is a complete description of the preferred embodiment ofthe present invention, it is possible to use various alternatives,modifications and equivalents. Therefore, the scope of the presentinvention should be determined not with reference to the abovedescription but should, instead, be determined with reference to theappended claims, along with their full scope of equivalents. Anyfeature, whether preferred or not, may be combined with any otherfeature, whether preferred or not. In the claims that follow, theindefinite article “A”, or “An” refers to a quantity of one or more ofthe item following the article, except where expressly stated otherwise.The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase “means for.”

1. A substrate support apparatus, comprising: a Z stage plate; a stagemirror; one or more actuators attached to the Z stage plate, wherein theone or more actuators are configured to impart movement to the stagemirror in a Z direction as the Z stage plate is moved in one or moredirections in a plane perpendicular to the Z direction, wherein the Zdirection is a vertical direction that is normal to an X direction and aY direction; and a substrate chuck mounted to the stage mirror withconstraints on six degrees of freedom of movement of the substratechuck; wherein the one or more actuators include one or more forceflexures wherein each force flexure includes: a base portion attached tothe Z stage plate; and a cantilever portion extending in a lateraldirection from the base portion, wherein the cantilever portion includesa parallelogram flexure coupled between the base portion and a free endof the cantilever portion.
 2. The apparatus of claim 1 wherein the baseportion and cantilever portion are integrally formed from a single blockof material.
 3. The apparatus of claim 1 wherein the base portion andcantilever portion are made of titanium.
 4. The apparatus of claim 1wherein the parallelogram flexure includes an upper arm spaced along theZ direction from a lower arm, wherein the upper arm is connected to thebase portion by a first resilient hinge and connected to the free end bya second resilient hinge, wherein the lower arm is connected to the baseportion by a third resilient hinge and connected to the free end by afourth resilient hinge.
 5. The apparatus of claim 4, wherein theparallelogram flexure further comprises a lever block located betweenthe upper and lower arms, wherein the lever block is attached to theupper arm between the first and second hinges.
 6. The apparatus of claim5, further comprising an actuator operably coupled between the baseportion and the lever block such that exertion of a force by theactuator against the lever block in the lateral direction causes thefree end to move in the Z direction.
 7. The apparatus of claim 6 whereinthe actuator is a piezo electric actuator.
 8. The apparatus of claim 7wherein the piezoelectric actuator includes a joint with a curvedsurface, the joint being located at an end of the piezoelectric actuatorsuch that the curved surface abuts the lever block.